The principle of the Plasma Enhanced Chemical Vapor Deposition (PECVD) is to utilize a radio frequency (RF) to ionize a reactive gas into plasmas, and then form a film on a substrate by reaction. More particularly, first, the reactive gas enters from a backplane and passes through gas diffusion holes, and is ionized into plasmas under the action of the radio frequency; and afterwards, reactive ions and groups in the plasmas react to form a thin film on the substrate carried by a substrate bearing table. The substrate bearing table, a component of a plasma enhanced chemical vapor deposition device, provides a gas diffusion hole installation platform, which is connected with a chamber cover via a sealing ring. The chamber cover and a cavity constitute the whole chamber via the sealing ring to provide a space and vacuum environment required for coating.
Gas diffusion holes are distributed in an upper electrode included in the PECVD device, the size of the aperture of the gas diffusion holes has a great influence on the homogeneity of film formation, and therefore, it is often necessary to measure the size of the aperture of the gas diffusion holes in the upper electrode (for example, after the maintenance of the upper electrode is completed).